AB1338 CALPROTECTIN, A SENSITIVE MARKER OF INFLAMMATION, IS ROBUSTLY ASSESSED IN PLASMA FROM PATIENTS WITH ESTABLISHED RA BY USE OF DIFFERENT LABORATORY METHODS
Authors: H. B. Hammer, S. L. Pedersen, I. Gehring, L. Mathsson-Alm, J. Sexton, J. Askling
Journal: Annals of the Rheumatic Diseases (2022)

Background Calprotectin (S100A8/S100A9, MRP8/MRP14) in plasma has been shown to be more sensitive than C-Reactive Protein (CRP) or Erythrocyte Sedimentation Rate (ESR) in reflecting inflammatory activity in patients with rheumatoid arthritis (RA). 1,2 Objectives The present objective was to explore the robustness of laboratory examination of calprotectin by comparing the results from assessments by use of two different methods. Methods Frozen plasma samples from a study of 177 patients with established RA initiating biologic disease modifying drugs were analysed for calprotectin levels at baseline and after 1, 2, 3, 6 and 12 months by use of either enzyme-linked immunosorbent assay (ELISA) or fluoroenzyme immunoassay (FEIA). The ELISA technique used kits from Calpro AS (Oslo, Norway) and the samples were assessed in a semi-automatic analysis machine Dynex DS2 (Dynex Technologies, Virginia, USA) at Diakonhjemmet hospital. The Calpro AS kits included all necessary buffers, cleansing solutions, enzyme substrate, standards, and controls (high and low calprotectin levels) and their protocol was used for the calprotectin assessments. The standards and controls were used as the mean of two measures, while all the patient samples were analysed as single measures. As a sub-study in NORA (a study exploring personalized medicine in RA by including several study cohorts from the Nordic countries), the same plasma samples were additionally assessed by FEIA. The FEIA technology used the EliATM calprotectin 2 wells in a Research Use Only setting on the PhadiaTM 2500 instrument (Phadia AB, Uppsala, Sweden) with a 1:50 dilution. Spearman was used for correlation assessments. To explore differences across concentration levels the baseline calprotectin levels were divided into 3 groups based on results from the Calpro AS assay (normal levels; ≤ 910 µg/L; moderately elevated; 911-2000 µg/L, highly elevated; &gt; 2000 µg/L). Results A total of 917 samples from the 177 patients (mean (SD) age 52.9 (13) years, disease duration 10 years (ranging from a few months to 46 years), 81% women, 78% anti-CCP IgG positive and 81% RF IgM positive) were included. The median of the correlation coefficients between the two methods at the six visits was 0.96 (range 0.91-0.97). Correlations were very high for normal levels (0.91) but somewhat lower for moderate and highly elevated levels (0.85 and 0.79, respectively). There were no significant differences between the associations depending on age, sex, or disease duration, nor on the anti-CCP IgG and RF IgM status of the patient. Conclusion The present study supports the robustness of calprotectin analyses, showing similar results across two different analytical methods, and that the concentrations were not influenced by demographic or immunological variables. Being a robust and more sensitive marker of inflammation than the commonly used CRP and ESR, calprotectin analyses should be available for assessments of RA patients in routine clinical care. References [1]Hammer, H.B., et al., Calprotectin (a major leucocyte protein) is strongly and independently correlated with joint inflammation and damage in rheumatoid arthritis. Ann Rheum Dis, 2007. 66(8): p. 1093-7. [2]Hilde Haugedal Nordal HH et al. Calprotectin (S100A8/A9) has the strongest association with ultrasound-detected synovitis and predicts response to biologic treatment: results from a longitudinal study of patients with established rheumatoid arthritis Arthritis Research &amp; Therapy (2017) 19:3 Disclosure of Interests Hilde Berner Hammer Speakers bureau: AbbVie, Lilly and Novartis, Sigve Lans Pedersen: None declared, Isabel Gehring: None declared, Linda Mathsson-Alm: None declared, Joe Sexton: None declared, Johan Askling Grant/research support from: AbbVie, AstraZeneca, Bristol Myers Squibb, Eli Lilly, Janssen, Merck, Pfizer, Roche, Samsung Bioepis, Sanofi, and UCB